The overall objectives of this project are to understand the endocrinology of the human glycoprotein hormones, thyroid-stimulating hormone (TSH), choriogonadotropin (hCG), luteinizing hormone (LH), and follicle-stimulating hormone (FSH),and thereby to develop diagnostic and therapeutic clinical applications. Recent research advances in the current period include the following: 1) Structure-function studies of the beta-subunits of TSH and FSH have identified domains important in the biologic properties of these hormones. Mutations at the glycosylation recognition site of the TSH beta-subunit diminished hormone secretion whether or not glycosylation was prevented, whereas carboxyterminal truncation stimulated hormone secretion. Mutations at the first glycosylation recognition site of the FSH beta-subunit dramatically increased receptor binding affinity, while paradoxically reducing intrinsic steroidogenic activity, again whether or not glycosylation was prevented. These novel findings identify the conformation of the beta-subunit polypeptide domain bearing carbohydrate as critical to the biological properties of glycoprotein hormones; 2) Human pituitary cell lines expressing the mRNA for the alpha-subunit and beta-FSH subunit have been established. These cell lines of gonadotroph lineage are expected to be a valuable model for study of human glycoprotein hormone synthetic mechanisms and investigation of GnRH receptor structure and function; and 3) Careful study of the pituitary- thyroid axis in 56 growth hormone deficient children has demonstrated the value of the nocturnal TSH surge test in the management of these patients. Hereafter, direction of the project will emphasize study of the structure-function relationships of FSH and the human FSH receptor through site-directed mutagenesis of their respective genes and investigation of signal transduction mechanisms in human thyrocyte follicles in vitro with analogs of hCG.